There are various types of cartilage, e.g., hyaline cartilage and fibrocartilage. Hyaline cartilage is found at the articular surfaces of bones, e.g., in the joints, and is responsible for providing the smooth gliding motion characteristic of moveable joints. Articular cartilage is firmly attached to the underlying bones and typically measures less than 5 mm in thickness in human joints, with considerable variation depending on joint and site within the joint. Additionally, articular cartilage is aneural, avascular, and alymphatic. In adult humans, cartilage derives its nutrition by a double diffusion system through the synovial membrane and through the dense matrix of the cartilage to reach the chondrocyte, the cells that are found in the connective tissue of cartilage.
Adult cartilage has a limited ability of repair; thus, damage to cartilage produced by disease, such as rheumatoid and/or osteoarthritis (OA), or trauma can lead to serious physical deformity and debilitation. Furthermore, as human articular cartilage ages, its tensile properties change. For instance, the superficial zone of the knee articular cartilage exhibits an increase in tensile strength up to the third decade of life, after which it decreases markedly with age as detectable damage to type II collagen occurs at the articular surface. The deep zone cartilage also exhibits a progressive decrease in tensile strength with increasing age, although collagen content does not appear to decrease. These observations indicate that there are changes in mechanical and, hence, structural organization of cartilage with aging that, if sufficiently developed, can predispose cartilage to traumatic damage.
Depending on the severity of the damage, affected joints may require surgical intervention. In some instances portions of the joint are sutured together to facilitate healing. In other instances, total joint replacement is necessary. In still other instances, implants short of total replacement are inserted. For example, U.S. Pat. No. 6,080,194 to Pachence et al. discloses a porous collagen-based implant for use in the repair of cartilage lesions. Specifically, Pachence proposes using a porous collagen sponge with a dense collagen membrane. The dense collagen membrane is provided as a barrier against movement of cells from the subchondral plate while the sponge permits the ingrowth of cells. U.S. Pat. No. 6,602,294 B1 to Sittinger et al. proposes implantable substrates for the healing and protection of connective tissue, preferably cartilage. The substrate includes a growth and differentiating factor, a chemotactic factor, a cellular adhesion molecule and a structure such as hydrogel or a sponge. U.S. Pat. No. 5,842,477 to Naughton et al. proposes methods for repairing cartilage by implanting a biocompatible scaffold in combination with periosteal and/or perichondrial tissue to provide a source of chondrocyte progenitor cells, chondrocytes and other stromal cells for attachment to the scaffold.
While many approaches to treat injured joints involve the surgical insertion of an implant, others have proposed the direct transfer of endogenous tissue housing synovial cells, without the need of an additional substrate. For instance, U.S. 2002/0122790 to Hunziker proposes the treatment of cartilage defects including surgically removing sheets of synovial tissue from the patient and introducing the entire sheet at the site of defect. While this approach effectively transfers synovial cells, additional beneficial cells or factors absent in the normal synovium must be added to advance the technique, which includes further surgical processes or culturing techniques.
Accordingly there remains a need to identify alternative approaches to the treatment of damaged or diseased tissue, which delivers a cocktail of beneficial cells, tissues or factors that together enhance recovery from surgical procedures. Further, there remains a need to effectively harvest these beneficial components and deliver them to sites requiring the generation of new tissue.